Beater wheel mill



April 17, 1962 P. RAETZ BEATER WHEEL MILL Filed oct. 21. 1959 ih intimi A,

IINVENTOR z PAUL RAETZ Bfm/ ATTORNEY nited States Filed Oct.l 21, 1959, Ser. No. 847,755 6 Claims. (Cl. 241-186) This invention relates -to a ybeater wheel mill in which material is pulverized by rotating a beater wheel or rotor Within a housing or casing at high speeds. The invention is particularly concerned with the type of mill wherein the ground material entrained in carrier gas is discharged from the mill by centrifugal force by way of an outlet duct, More specilically, the invention pertains to improvements lbuilt into the outlet duct and mill outlet casing for separating the coarser particles from the fines and returning the former to the mill for regrinding.

In mills of this type, as commonly practiced, the conveying gas and material mixture is conducted from the mill into ya reverse flow separator, cyclone classifier or sifting screen, in which the oversized or coarseparticles are separated from the mixture and are returned to the mill for further grinding -by being passed again through the beater wheel. These separators, classifiers or screens represent a substantial investment and a significant portion of the origin-al cost of the mill. Furthermore, they contribute to higher operating and maintenance costs by substantially increasing the flow resistance through the mill system. These disadvantages are especially disturbing because, due to the high grinding eciency of this type of mill, only small quantities of oversized material are carried in the conveying gas leaving the mill, so that in many cases the relatively high outlay for additional separating apparatus cannot be justified.

In accordance with the invention these conditions can be considerably improved by providing the outlet of the mill with Aa front wall portion inclined for directing the stream of carrier gas and entrained pulve'rized material transversely of the duct vand toward a depression, pocket or niche provided in the duct wall opposite and above the inclined front wall portion. Due to inherent inertia 4 forces, the oversized or coarser particles entrained in the gas stream are thus carried into the pocket or niche, whereas the conveying gases with the nely pulverized material remaining therein is drawn off past the niche and out through the outlet duct to a place of use. The separated coarse particles fall back into the beater wheel for further grinding.

ln order to prevent the separated particles to be 'caught up again in the dust conveying gas stream while returning to the mill casing, an adjustable Wall is provided, according to the invention, for shielding these returning particles from the upwardly flowing gas stream. This adjustable wall terminates in close proximity of the beater wheel, extends up to the base of the pocket and is spaced from the rear wall of the outlet gas duct to form a convenient return passage for conducting the coarse particles to the mill housing. By adjusting the position of this Wall with respect to the front wall of the gas outlet the velocity of the gas stream leaving the mill outlet can be altered at will thereby influencing the size of the particles captured in the pocket. If the material to be ground is of extremely friable nature and can readily be pulverized to the desired iineness, or when a coarse mixture is desired, the invention contemplates that the pocket i are or niche be equipped with a rear Wall section acting as a flap or door that is movable inwardly in a direction toward the gas stream. in this manner the pocket can be partially or completely covered or closed by the door to control the degree of particle separation desired or to eliminate separation entirely.

Further, in accordance with the invention, one or more openings are provided at the lower end of the above adjustable pocket door or flap to permit lany material accumulated between the pocket door and the rear casing to drop Iback into the mill housing.

ln addition, the invention contemplates the provision of `an inward enlargement, extension or thickening of the rear duct casing to till and occupy the above-mentioned opening or cut-out in the flap door when the door is in the uttermost rearward or fully open position. ln this manner an unbroken and smooth inside surface of the duct can be presented to the flow, thereby eliminating depressions which may favor undue Wear of the inside wall surface Iby the formation of eddy current.

Further details and objectives of the invention will become apparent from the drawing and the foll wing description thereof. In the drawing:

FlG. l is Ian elevational section through a beater mill equipped with the herein disclosed improvements, when taken on line lof FIG. 2;

FIG. 2 is an elevational section taken through the improved beater rnill on line 2-2 of FIG. l;

FlG. 3 is an enlarged View taken along lines 3-3 of FIG. l and showing the lower end of the adjustable door or flap of the herein disclosed pocket formation;

FIG. 4 is an enlarged cross section taken on line 4-4 of FG. 3.

Referring to FIG. l the illustrated mill is provided with a beater wheel i0 serving simultaneously as the rotor of a blower. The beater wheel comprises a wheel disc l, an annular disc i2, spaced therefrom and a plurality of radial beater plates 14 arranged between discs 1l and l2 and equally spaced around the circumference of the beater wheel. An overhung shaft 16 jou-rnaled in a bearing 18 serves to support the beater wheel or rotor l0 for horizontal rotation and is connected to a conventional driving means, not shown, by way of a coupling 20. The beater wheel 10 rotates within a housing 22 in direction of arrow 23. The preferred Shape of housing 22 is that of a spiral gradually expanding in direction of rotation and terminating in a generally vertical outlet duct 24. This duct, preferably located directly above the rotor 10 has a vertical front wall portion 26 with the lower end thereof being connected to the spiral housing by an inclined wall extension 28. The inclination of this wall with respect to the vertical continuation of duct 24 is toward the axis of rotation, and such as to cause the stream of pulverized material entrained in the carrier gas to be deflected transversely of the duct 24 and in direction toward a pocket or niche 30 provided in the rear wall of duct 24. This pocket 30 is defined by an upper horizontal wall 32 and an adjustable door or flap 34 pivotally supported at the lower end thereof at 36. A positioning device such as notched bar 33 enables the operator to adjust the position of flap 34 from a rearward or open position as shown in solid lines with flap 34 in close proximity of outer rear casing 40, to ya forward or y closed position as shown in dot and dash lines, With the flap door shutting off the pocket 30 and eliminating the eifect thereof. A series of notches in the bar bearing si) against a stop plate 31 enable the operator to position flap 34 at other locations intermediate the above two extreme positions, so as to control the effectiveness of pocket 30 in capturing oversized particles entrained in the gas stream.

The captured coarse particles are returned to the mill housing to the grinding action of the beater wheel by way of a passage 42 formed in the outlet duct 24 directly below pocket 30. Passage 42 is defined by an adjustable division wall 44 separating and shielding the returning coarse particles from being re-captured by the upwardly flowing gas stream. The lower end of division wall 44 can be pivoted at 46, which pivot can be of the fixed type or the position thereof can conveniently be adjusted in a slot 47 provided in each of the side walls of duct 24. Notched bar 48 and stop plate 49 or other suitable device permits adjustment of the angularity of Wall 44 with respect to inclined wall 28, so asto increase or decrease the flow area of the outlet duct for the purpose of decreasing or increasing respectively the velocity of the gas stream. In this manner the size of coarse particles captured in pocket 30 can be influenced and with it the fineness of the pulverized material leaving duct 24.

FIGS. 3 and 4 show an opening 50 provided in the lower end of flap 34 for permitting any material caught behind the flap while in an intermediate or forward position to drop back into the mill. There is also shown a filler piece 52 which occupies the opening 50 when the flap 34 is in the most rearward position as shown in solid lines in FIGS. l, 3 and 4. A smooth and uninterrupted surface is thereby produced which reduces possible wear cf the surface due to the formation of eddy currents. While opening 50 has been shown as being provided in the lower end of door 34 other openings could be provided along the side door 34 which would serve the same purpose of permitting trapped material to leave the pocket while the door is closed.

While I have illustrated and described a preferred embodiment of my novel organization, it is to be understood that such is merely illustrative and not restrictive and that variations and modications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

l. In a beater mill, a housing, a rotor within said housing rotatable about a horizontal axis and adapted for pulverizing material by attrition and impact, means for receiving material to be pulverized and carrier gas into said housing, an outlet duct leading from said housing for expelling by centrifugal force a stream of carrier gas and pulverized material entrained therein, said duct having a wall inclined for directing said stream transversely of the duct, means forming a pocket in the duct wall opposite and above said directing wall for capturing oversized particles contained in said stream, a passage generally parallel to said outlet duct leading from said pocket to said housn ing, and a deflecting surface included in the uppermost wall portion of said pocket for deecting said captured oversized particles toward said outlet duct for returning said particles to the mill for further grinding, said passage having an adjustable wall spaced from said inclined wall and common to said outlet duct, means for adjusting the spacing between said adjustable wall and said inclined wall to increase or decrease the velocity of said transversely directed stream.

2. In a beater mill, a housing, a rotor Within said housing rotatable about a horizontal axis and adapted for pulverizing material by attrition and impact, means for receiving into said housing material to be pulverized and carrier gas, a generally upright outlet duct leading from said housing for expelling by centrifugal force a stream of carrier gas and pulverized material entrained therein, said' upright duct including a wall section inclined to the vertical for directing said stream transversely of said upright duct, means forming a triangular` pocket in the duct wall opposite and above said directing wall for capturing oversized particles contained in said stream, said pocket having an adjustable door hinged at the lower corner of said triangular pocket, means for moving said adjustable door inwardly in a general direction opposed to said transversely directed stream, to reduce the size of said pocket and thereby reduce the effectiveness thereof in capturing said oversized particles and a passage leading from the hinged corner of said pocket to said housing for returning said oversized particles to the mill for further grinding.

3. The improvement in a beater mill as dened in claim 2, wherein said adjustable hinged door is provided with an opening at the hinged lower end thereof to permit escape of captured particles while the door is in the inward and forward position.

4. The improvement in a beater mill as defined in claim 3, wherein an extension or filler is provided in said opposite duct wall to fill said opening while said adjustable rear wall is in the rearward position.

5. In a beater mill, a casing having an involute outline, a beater wheel within said casing rotatable on a horizontal axis and adapted for pulverizing material that is being fed to the mill in a gas stream, said casing having an upright outlet duct positioned above said horizontal axis for tangentially discharging a stream of pulverized and gas entrained material, the lower front wall portion of said outlet duct directly adjoining said involute casing and being inclined toward said axis for directing said stream transversely of said duct, an adjustable division wall opposite said front wall portion and generally parallel thereto for dividing said duct into a forward passage adjacent said front wall portion and a rearward passage remote therefrom, means for adjusting the angularity of said division wall with respect to said front wall portion for restricting the dow area of said forward passage and enlarging the ow area of said rearward passage at the upper ends thereof, said outlet duct being provided with a pocket above said rearward passage for capturing oversized material entrained in said transversely directed stream, said pocket being defined by a roof surface for deecting oversized particles downwardly towards said rear wall passage and means for returning oversized particles back into said casing via said rearward passage.

6. In a beater mill, a casing having a curved outline, a beater wheel within said casing rotatable on a horizontal axis and adapted for pulverizing material that is being fed to the mill in a gas stream, said casing having an upright outlet duct positioned above said horizontal axis for tangentially discharging a stream of pulverized and gas entrained material, said outlet duct including a lower front wall portion adjoining said curved casing and being inclined toward said axis for directing said stream transversely of said duct, an adjustable division wall opposite said front wall portion and generally parallel thereto for dividing said duct into a forward passage adjacent said front wall portion and a rearward passage remote therefrom, pivoting means for supporting said division wall at the lower end thereof, means for adjusting the angularity of said division wall with respect to said front wall portion for restricting the ow area of said forward passage and enlarging the flow area of said rearward passage at the upper ends thereof, said outlet duct being provided with a pocket above said rearward passage for capturing oversized material entrained in said transversely directed stream, said pocket including an upper deiiecting surface for deccting oversized particles back into said casing, via said rearward passage, said pocket having a substantially upright door to shield at least a major portion of said deecting surface, pivoting means supporting said door at the lower end thereof for swinging the upper end of said door forward to decrease the size of said pocket and accordingly the effectiveness thereof in returning oversized particles back into said mill casing for further grinding.

References Cited in the le of this patent UNITED STATES PATENTS 5 @$059 553,163 Jolicard Jan. 14, 1896 1,178,784 1,449,169 Elzemeyer et a1. Mar. 20, 1923 6 FOREIGN PATENTS Great Britain Aug. 6, 1929 Germany May 27, 1941 Germany Feb. 2, 1943 Great Britain Jan. 28, 1959 France Dec. 15, 1958 

